One of the most important conditions defining correct machinery operation is regular bearing lubrication. The insufficient amount of a lubricating material (or a lubricant) or an incorrectly chosen lubricating material inevitably leads to early bearing wear and loss of bearing service life, as well as inefficient operation and unnecessary energy waste.
Lubrication determines bearing longevity on equal terms with a bearing material. The role of lubrication has especially become more essential with the advent of complex friction assemblies, such as vehicle engines, turbines, electrical motors, rotors, machineries, etc., and with the increase of their operation intensity consisting in raising rotary frequencies, loads, and temperature.
The primary function of a lubricant is to reduce friction between two moving solid state surfaces by providing a uniform lubricant layer in the space separating them. Typically, lubricant-to-surface friction is much less than surface-to-surface friction in a system without any lubrication. Thus, the use of the lubricant reduces the overall system friction.
As a result of friction reduction, the lubricant may reduce the amount of wear that occurs during operation, reduce operating temperatures, minimize corrosion of metal surfaces, and may assist in keeping contaminants out of a bearing system, and improves system efficiency. Lubricants have many properties that can be mixed and matched to meet different operating needs. For example, there are different chemicals that can be added to allow a machinery to efficiently run at extreme temperatures. The lubricant can also be made more effective in protecting machinery surfaces under extreme pressures. By looking at the demands of the machinery, one can properly identify the type of lubricant best suited for its proper function.
Traditionally, various techniques can be utilized to perform bearing lubrication using proper lubricants. Conventional devices for providing lubrication include port holes, grease packs, oil slingers, hydraulic pumps, and others. Port holes are generally machined radially through input shafts for ducting oil inwardly to bearings. Grease packs are simply large masses of grease in which pocket bearings are packed during assembly of machineries. Oil slingers and hydraulic pumps involve mechanical pumping actions for providing forced oil flow to bearings.
Port holes are deficient in high speed lubrication of input shafts because oil travels inwardly to bearings only during slow rotation or stoppage of shafts. At high rotation speeds, centrifugal forces throw the oil outwardly rather than inwardly through the port holes, thus starving bearings at high speeds when lubrication becomes more critical.
Grease packs are successful at low speeds and under low loading conditions. However, under increased speed and loading conditions grease packs deteriorate rapidly and are, therefore, unsuitable for long-term bearing lubrication.
Oil slingers and hydraulic pumps are more successful than port holes and grease packs under high speed and load conditions. However, slingers and pumps are generally more expensive, and often work against rather than with centrifugal forces in the movement of lubricant to bearings. In addition they typically require either a separate or derived power source, thus reducing overall system efficiency.